The study of programming languages is central to the study of computer
science. When studying a programming language, one must
learn both the syntax and the semantics of the language in order to
understand it, rather than simply be able to use it. Everyone knows
and agrees upon what is meant by the syntax of a language, but
what do we mean by “semantics” ? What one requires of a description
of the semantics of a language is dependent upon one’s point of
view. A compiler writer is happy with a description of the operational
semantics of a language; someone interested in proving properties
of a given program might prefer to use the axiomatic
semantics of the language. A language designer, being as concerned
with what can be said as with how to say it, may prefer a denota-
Preface
tional (mathematical) description. The denotational description is
also most useful when attempting to prove the equivalance of different
implementations of the same language.